The Toughest Animal You Can't See

Among the most resilient creatures on Earth is one barely visible to the naked eye. The tardigrade, sometimes called a water bear, is a chubby, eight-legged animal smaller than a grain of sand. It lives in mossy patches, ocean sediments, and the films of water that cling to soil. What makes the tardigrade remarkable is its response to harsh conditions. When its surroundings dry out, the animal expels nearly all the water from its body and pulls in its legs, shriveling into a dormant ball called a tun. In this suspended state its metabolism almost halts, and it can endure temperatures near absolute zero, the vacuum of space, and doses of radiation that would kill most life many times over. Years later, a single drop of water can revive it, and the tiny animal lumbers off as though nothing had happened. Scientists study tardigrades to understand how life might survive on other worlds, and how delicate biological structures can be preserved through extreme stress.